Stone asphalt road and method of preparing and laying the same



Dec. 21 1926.

1,611,444 D. MQK. HEPBURN STONE ASPHALT ROAD AND METHOD OF' PREPARING AND LAYING THE SAME Filed Nov. 5. 1925' 2 Sheet-Sheet 1 run:

Dec. 21 1926. 1,611,444

D. M K. HEPBURN STONE ASPHALT ROAD AND METHOD OF PREPARING AND LAYING THE SAME Filed Nov. 5. 1925 2 Sheets-Sheet 2 WWI/ Patented Dec. 21, 1926.

UNITED STATES- PATENT OFFICE.

DONALD MOKNIGHT HEPBURN, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO AMIESITE ASPHALT COMPANY OF AMERICA, OF PHILADELPHIA, PENNSYLVANIA,

A CORPORATION OF NEW JERSEY;

STONE ASPHALT ROAD AND METHOD OF PREPARING AND LAYm'G THE SAME.

Application filed November 55, 1925. Serial No. 66,586.

My invention relates to bituminous road surfacing materials or Compounds and to the manufacture thereof, the said materials being of such character that they can be mixed at the quarry where the stone originates or where the aggregate-originates, and

can be'shipped in railroad cars, or trucks over the highways, and can be laid at the temperature of the air without any further preparation, or may be held in storage to be employed at any future time without further preparation. In accordance with the invention the stone or other aggregate is dried and cleaned and prepared for the storing or absorption of a solvent therein before the aggregate comes into contact with the bitumen which is to be used as a binder. This drying and cleaning is done without substantially heating the stone or aggregate and thereafter the solvent is added. After the' solvent has been absorbed by the stone, the latter is mixed with the bitumen. The solvent contained in the stone is then slowly absorbed by the cold bitumen which is by this means maintained in a plastic condition. The thorough drying of the stone by my process gives me ample-capacity of storing the amount of solvent-required to handle the material at the temperature of the air, and the reabsorption of the solvent from the stone into the bitumen extends over a period of many days or even weeks. The material manufactured by this method can thus be shi ped long distances and successfully unloaded and laid in place at the temperature of the air. I have in actual practice shipped the material hundreds of miles, taking 10 days or more in transit, and have experienced no trouble in unloading or laying. The materials permit the road surface to be produced with any finish or texture desired for non-skid surfaces.

In view of the foregoing, it will be understood that one of the principal objects of the invention is to provide a road of improved character.

Another object of the invention is to provide a method of road laying whereby my improved road may be constructed.

Still. another obect of the invention is to provide a slow setting bituminous stock material for road making or surfacing which material is adapted to be transported and laid at atmospheric temperatures and without any preliminary heating. A further important object of the invention is to provide an improved method for mixing or manufacturing the improved road surfacin material.

\ Further ob ects of my invention will'be apparent from the 'following specification and claims.

In the accompanying drawings, I have shown a road constructed in accordance with my invention, and I have also shown diagrammatically an apparatus whereby my improved method may be carried on. It is to be understood, however, that the drawings are for illustrative purposes'only and are not to be construed as defining or limiting the scope ofthe invention, the claims forming a part of this specification being relied upon for that purpose,

Of thedrawings:

Fig. 1 is a transverse sectional view showing the laying of the first course of material toform a road embodying the invention.

Fig. 2 is a view similarto Fig. 1, but showing the laying, of the second course of material.

Fig. 3 is a'transverse sectional view showing the completed road embodying the invention.

Fig. 4 is an enlarged fragmentary sectional view showing the relation between the stones of the second or wearing course of material and the third or sealing course.

Fig. 5 is adiagrammatic view of an apparatus whereby my improved method of spectively for three separate courses in the construction of the road. There are two different sizes of stone for the first two courses, and a coarse sand is used for the third or sealing course.

For the first course I preferably use run of crusher stone which has been screened through a one' and one-half inch screen, that is, a screen having circular openings one and one-half inches in diameter, and

which has been retained in a three-quarter inch screen, that 1s, a'screeu w th circular openings three-quarters of an inch in diameter. It is important to select a grade of stone that fractures in cubes or similar shapes and not in flat thin wafers. For the second course I preferably use all sizes that pass through a three-quarter inch screen, and which are retained on a one-quarter inch screen. For the top or sealing course, I use good, sharp river or concrete sand which will pass a one-quarter inch screen.

lVhile I do not limit myself to the exact sizes specified, I nevertheless consider it very important that the size limits be properly related; It will be noted that the upper size limitfoi' the first course is twice that for the second course, and approximately this ratio should be maintained, even though the sizes themselves be changed. It will further be observed that the lower size limit for the first course is the same as the upper limit for the second course, and that the lower limit for the second course is the same as the upper limit for the third course.

All of the three grades of material used in my pavement are separately mixed with a bitumen, preferably in accordance with the method to be described, and -are then placed on the foundation in three separate courses. As shown in 1, the base course 12 is placed on the roadway first, about two and one-quarter inches of loose material ordinarily being used, and the material is then rolled or compressed to about one and one-half inches .in thickness when thoroughly compacted. The quantity of binder in the first course is such as to avoid any excess thereof.

Asshown in Fig. 2, I lay on the base the second course 12 or wearing course 13,

'which is raked uniformly over the said About one inch of loose mabase course. terial is ordinarily applied which is then compressed to about one-half inch in thickness making a total depth of the material of about two inches. The quantity of binder in the second or wearing course is such that after compacting the stones will project.

The thicknesses of the two main courses, while preferably approximately" as given, ma vary widely according to circumstances, an the drawings. The showing of the road roller is entirely diagrammatic and not to scale. \Vhere the pavement is to be laid in city streets the size of the stones in the wearing surface can be changed to a maximum size of five-eighths inch, caught on onequarter inch screen. When the pavement is to be laid thicker than two inches, the size of the stones in the base course can be correspondingly increased.

I place the third or sealing course 14 on the wearing course, to form the complete pavement as shown in Fig. 3. The quantity of binder in the material for the sealing somewhat thicker courses are shown in course is such that the material is granular in character and can be easily spread. A small amount is placed on the surface of the wearing course and then is raked or hoed,

with the edge of a board or a back of a rake, over the wearing surface, so that none of the sealingor third course projects above the highest pieces of aggregate in the second course. This is clearly shown in Fig. 4. When the third or sealing course 14 has been distributed in this manner, the road is opened to trafiic without any'rolling of the third course; The wheels of the traflic compress the third or sealing course tightly between the small pieces of aggregate of the wearing course and seal the roadway tightly together, making the same waterproof. In this way the road is sealed without covering up the grain or texture produced by .the second course, and the second or wearmg course is left exposed in its best non-skid condition. Thus by my novel method of sealing and water-proofing the road, I have added a sealing coat without destroying the non-skid surface of the wearing course. I

In all .asph'altic concrete mixtures or sheet asphalt mixtures, the sand is carefully graded and a certain definite amount of nes passing a two hundred mesh screen are absolutely essential for the proper mixture. In my process I purposely keep the .fines out of the first and second course material having no material finer than threequarter inch in the basecourse and no material finer than one-quarter inch in the lwe-aring surface. It will be seen that my improved road composition is not an asphalticconcrete nor a sheet asphalt nor a ituminous macadam, bein radically different from all of these; t includes only stones or other pieces of aggregate of selected and restricted sizes and is entirely free from fines.

A road constructed in accordance with my invention is rigid and stable to an unusual degree. This is due in large part to the fact that each of the two maln courses comprises stones of a considerable size range without, however, including the small fines and chips. The stones in each layer intermingle and pack when coated with a heavy coat of bitumen and when properly rolled or compressed together. Thus I have roper stability for supporting the wheels 6 traffic without the aid of a hard bitumencement. The road is also wave proof and roll proof, a characteristic not obtained in any other type of pavement,'where all the voids are not completely filled with smaller sizes of aggregate and bitumen. Although my pavement contains a plastic cement, it will not affect it,

A further advantage of my improved road construction is that the peculiar surface provided entirely eliminates the hum- I one or even two of them may be omitted.

For example, I find in actual practice where the road to be"surfaced is of the rigid type, such as concrete, etc., that it is'necessary to apply only two courses. The wearing surface and sealing course can be used exactly in the manner described above, except that the wearing surface is to be placed one inch thick when compressed. The sealingcoat is to be added exactl as'described above. In

other cases the sea ing coat may be entirely the crushed rock or other aggregate which is to be used. As illustrated this drum is inclined to enable the material to-progress through it. Suitable means, such as a motor 2, is provided for rotating the drum.

An elevating conveyer 3 is provided for delivering the crushed rock or aggregate to the receivlng end of the drum. Before being delivered to the conveyer the rock or other aggregate is suitably graded as to size by screens or other devices which are not shown.

porting means, such as a railwaycar 8.

- Air can be supplied to the lower end of the From the drum 1 the aggregate is discharged through a chute 4 into a weighing.

hopper 5, From the weighing hopper the aggregate is discharged into a suitable.

mixer 6 which may be provided with a steam-jacket 7 From the mixer the material can be discharged into asuitable transdrum 1 by means of a suitable fan 9. For

least some of the air, I

heater which is shown as ing an oil burner 10. ,Preferably I heat only a portion of the air suppliedto the fan and I, therefore,

provide. a funnel 11 through which the.

heated air is delivered, other air being drawn into the fan around the funnel.

' In practicing my improvedmethod, the stone is suitably raded as to size as already stated, and is t en delivered by the conveyor 3 'into the drum 1. By reason of the rotation of the drum, the aggregate is caused .,to slowly progress downward through the drum, and n doing so it is acted upon by the air dehvered'by the fan 9. In practice and fora drum four. feet in diameter I prefer a fan having a capacity of 'approximately 140,000 cubic feet of air per minute. a

This large volume of air flowing through the drum in opposition to the movement of the aggregate removes all dust and small ,the. aggregate as well as acleaning medium therefor, and to facilitate the drying action the air is-or'may be slightly heated. The heating means forjzhe air has already been described, and it will be understood that the fan serves to draw in a large volume of air directly from the atmosphere, and also serves to draw in-a smaller volume of highly heated air through the funnel 11. In ordi nary practice I have found that approximately one'cubic foot of heated air should be drawn, through the funnel for each twenty cubic feet. of air drawn directly from the atmosphere. The heated air and the atmospheric air are thoroughlymixed by .the fan with the result that the air mixture delivered into the drum is at a temperature .only slightly above that of the atmosphere.

I prefer to so control thetemperature 'of the aif delivered to the drum that the aggregatewill not be raised more than six or seven degrees above the atmospheric tem- 'perature.

I have found that in dry clear summer weather I can eliminate the burner for artificially heating the air, the required drying of the stone being effected by the atmospheric air without heating.

means of the weighing hopperdefinite B batches of the agregate of. predetermined weight can be. delivered to the mixer 6, and from the foregoing description it will be seen that the aggregatethus delivered has been thoroughly cleanedland thoroughly dried without, however,- having. the temperature thereof raised much above the atmospheric temperature. This, avoidance of any substantial -i'ncrease in-the temperature of the aggregate is important for a I reason which will presently appear. heating the air delivered by the fan, or at I rovide a'suitable As'soon as a batch of the aggregate is delivered into the mixer, which is in operation, I add to the aggregate a suitable material which is adapted to serve as a solvent for the asphalt or other bitumen which, is to besubsequently added. This. solvent should be a slowly volatile one such as kerosene or other oil having a flash test, or evaporatir? temperature, rangin from 120 degrees .to 150 degrees F. t will be seen-that I select a solvent which willnot rapidly'eva rate at atmospheric temperature, and w ch, therefore, will not within a reasonable time be caused to evaporate to any appreciable extent by reason of the con.- tact with the aggregate which, as'already stated, is at only a few degrees above the a so atmospheric temperature. The amount of solvent which is added is carefully predetermined by test so .that there will be no excess beyond what can be retained and absorbed by the thoroughly dried and slightly porous' surfaces of the stone. I have found that when the stone is thoroughly dried, as described, a considerable amount of solvent can be absorbed thereby, and the operation of the mixer is continued until all of the surfaces of the aggregate are thoroughly saturated with the solvent and until the solvent is completely absorbed.

After the solvent has beenabsorbed, I

i then preferably add a substance which serves to toughen or thicken the bitumen. This substance is preferably hydrated lime and I add from one-half to one percent by actual weight. The mixing is continued until a thoroughly homogeneous mass is produced, with the lime uniformly distributed as a surface coating over the pieces of stone or aggregate. I have found by actual practice that either causticilime or hydrated lime will produce the same results, but, inasmuch as the caustic. lime is harder to handle, I

V prefer to use the hydrated lime.

' the sealing course material.

stood that the heating of the bitumen is primarily for the purpose of more easily securing the required uniformity of mixture and the required uniformity of the distribution of the bitumen over the surfaces of the pieces of stone or aggregate. This heating is not for the purpose of facilitating the subsequent laying of the material, as the material is allowed to become cold before being laid.

The steam-jacket may be used for the purpose of maintaining the heat of the bitumen during the final mixing operation, but

is not used during the preliminary mixing operations when the solvent and the lime are added. After the mixing with the bitumen has been completed the mixture is then discharged from the'mixerinto the railway car 8 or other transporting means.

The hydrated lime which I add to the mixture of my material is used to toughen the binder, particularly at the points of contact with the stope- This also increases the thickness of the bitumen on the individual stones of the aggregate, a result that is very beneficial and desirable. The lime, being added before the. bitumen is added to the of both the aggregate and the bitumen to about 275 degrees F.; and third, the cold methods of combining the aggregate and bitumen by thinning the latter with a solvent, In the emulsifying method, the aggregate absorbs a large quantity of the water or, in other Words, becomes'saturated. As the result of this method a comparatively thin coat. of bitumen is left on the aggregate, and

the mixture has a very temporary life, with a relatively poor bond between the bitumen and the aggregate. By the hot mix method the heat, which is applied to both the aggregate and the bitumen, is used as a distributing agent to keep the material plastic; and the result is that the material must be placed and compacted in the pavement at a high temperature. By the method wherein the solvent is added to the as halt as a distributing agent, suflicient so vent must be added to handle the asphalt cold. This results in too thin a coat on each-individual stone in the aggregate.

From the foregoing 1t will be apparent that my improved process differs radically from prior practice in that I neither apply heat'to the entire mass to effect distribution nor add a liquefier to'effect distribution. I apply heat only to the bitumen, and mix this hearted bitumen with cold aggregate in order to obtain a thick coat of bitumen which is chilled in coming into contact with the aggregate. This gives me a thicker coating of asphalt on the individual pieces of aggregate than could, be obtained with hot stone. I store the solvent in the stone so that it is not used at all as a fluxing material or liquefier to aid in coating the stone. The solvent having been stored or absorbed in the aggregate before coating and the asphalt having been chilled when coated on the stone, I have a physical condition of the bitumen that holds the heavy coating on the stone. This bitumen, now being cold and far below the melting point thereof, is slowly attacked by the solvent and,

due, to thefactthat the bitumen and stone are cold, the action of the solvent is retarded and this facilitates the unloading and laying of the material days after the material has been mixed. I find in actual practice'- that the slow absorbing of the solvent by the bitumen tends to draw the bitumen further into the surface of the stone. Any solvent that is absorbed by the bitumen must be replaced by the bitumen enetrating the pores of the stone occupied y the solvent. This not only retards the action of the solvent but also increases the bond between the stone and the bitumen.

In case additional heat is needed in the final mixing to produce a uniform coating of the bitumen on the ag e ate, the steamjacket of the mixer is used By this method the bitumen absorbs the heat first and the minimum amount required is used, so as not to defeat the advantage gained by using the cold aggregate. In this way I get a thorough coating without the use of a liquefier in thebitumen or .heat in the aggregate. 1

Referring again to my improved pavement it will be understood that the base isrolled or compressed first, and that the wearroller having a wide contact with the pavement can roll a pavementmaterial to ultimate compression. With my method of manufacture, advantage is taken of the I trafiic over the road to compact the road and which consists in adding bring it to' ultimate compression, as the material is in its original cold and plastic condition so that it can benefit by the compression of traflic.

As to-some of its subject matter this application constitutes a continuation in I part of my cb-pending' application for road surfacing material and method of manufacturing and laying, Serial No. 11,367,

filed February 24 1925.

What I claim is:

1. The method of forming a roadway,

gate a slowly volatile bitumen solvent which is stored therein, the quantity of such-.sol-

' vent being limited to that which can be -absorbed by the surfaces of the stones,.mix-

ing with the aggregate bitumen in suflicient quantity to completely coat the stones thereof, laying the mixture on the roadbed to form a wearing surface, and compacting the said mixture upon the roadbed.

2. The method of forming a roadway,

, which consists in adding to a stone aggregate a slowly volatile bitumen solvent which 15 stored therein, the quantity of such solvent being limited to that which can be absorbed by the surfaces of the stones, maintaining the aggregate at approximately atmos= pheric temperature, munngwith the aggreto a stone aggrewearing surface, .and compacting the said mixture upon the roadbed.

3. The method of forming a roadway, which consists in adding to a stone aggregate a slowly volatile bitumen solvent, such as kerosene, the quantity of such solvent being limited to that which can be absorbed by the surfaces of the stones, adding a quantity of lime to 'the aggregate and distributing it as a coating over the surfaces of the stones thereof, mixing with the aggregate bitumen in sulficient quantity to completely coat the stones thereof, laying the mixture on the roadbed to form a wearing surface, and compacting the said mixture upon the roadbed.

4. The method of forming a .roadway, which consists in adding to separate stone .and sand aggregate a slowly volatile bitumen solvent which is limited in quantity to that which can be absorbed by the surfaces of the stones and of the sand particles, mixing bitumenwith the respective aggregate to completely cover the stones and particles thereof, laying the stone mixture on the roadway and compacting it to form a wearing surface, and sealing the wearing surface by partly filling the recesses therein with the sand mixture and without forming a coating on'the top of the wearing surface.

5. The method of mixing a bituminous paving composition consisting of applying a itumen solvent to the surfaces of pieces of stone constituting an aggregate, which solvent is limited in quantity to that which can be absorbed by the surfaces of the stones, adding a coating of lime to the surfaces of the pieces of stone, and subsequently adding a bitumen to the aggregate.

6. vThe method of mixing a bituminous paving composition consisting ofa'pplying a bitumen solvent. to the surfaces of pieces of stone constituting an aggregate, the said aggregate being at approximately atmospheric temperature and the said solvent being limited in quantity to that which can be absorbed by the surfaces of the stones, addiii) ing a coating of lime to the surfaces of the piecesv of stone, and subsequently adding heated melted bitumen to the aggregate which is maintained at or near the said atmospheric temperature until engaged by the bitumen.

DONALD MOKNIGHT HEPBURN. 

